The mission begins on a cargo train platform; head right and go through the train cars and take the stairs up to a walkway overlooking the platform. From this vantage point, eliminate as many zombies below as possible before proceeding to the stairs on the opposite end of the walkway. At the bottom of the stairs, go left and around the large cargo container and kill any zombies and Crimson Heads in the way. Work your way to the large cargo elevator and activate the marked control box to raise the lift; this will cause zombies and Crimson Heads to attack. Defend the platform until it arrives; when it does kill the zombies on the cargo lift and get on board, using the marked control box to send the lift down to the labs. The lift will stop twice on the way down; simply kill the zombies that attack you and activate the marked control boxes to reactivate the lift and continue down. Once the cargo elevator stops for the third time, exit the lift to trigger a cutscene.

Getting at Ada is extremely hazardous as the hallway before her is mined with laser trip mines in addition to her throwing incendiary grenades and firing down the hallway, which causes significant damage. The best way to handle this is to stay out of her sight as long as possible while shooting out as many of the mines as possible; unfortunately at least two of them are hidden behind crates and cannot be shot at from a distance. Use carefully placed grenades to set these last two mines off. Once the mines are neutralized, take cover and shoot Ada until she staggers, then run down the hallway and take cover behind one of the crates. Repeat this and keep jumping from cover to cover and get as close to her as possible; once in the same room as her a cutscene will trigger and Ada will retreat. Shoot out the two mines blocking your progress and follow her out of the room into a large open chamber; Spec Ops will attack. Once the soldiers are dead, head to the nav marker and soon enter a room filled with cargo containers and zombies; kill the zombies and search the containers for items then proceed to the nav marker and activate the cargo elevator.

Shortly after the elevator begins to descend a pack of Lickers attack; kill them and continue riding the elevator to the bottom where a group of zombies and parasite zombies await. Once the zombies have been dealt with, head right towards the nav marker.The team will enter a large furnace area; head right and then take the left ramp up to the second floor. Kill the Hunters you encounter, then head to the nav marked door on the left side down one of the ramps. Go through the door and into a small waiting room/lobby; take the stairs up and go down the left-side hallway and follow the nav marker to enter the lab's security room. Activate the security console to trigger a cutscene then head right and go through the door at the end of the room. Keep going and eventually you will emerge into another hallway and a group of zombies will attack. Once they are dead, go through the large marked doors to enter a huge lab room crawling with zombies. Occasionally Hunters will break out of the stasis cylinders found throughout the room; kill them and press on towards the marked door on the third floor to enter the small security room where the game began. Enter the marked elevator shaft and use the ladder to climb the shaft.

You will emerge in another furnace room and quickly be attacked by a group of Hunters; quickly run up the ramp to the marked ladder and use it to climb to the next level. Instead of hunters, now Crimson Heads attack. Wipe them out and head to the marked door on the left side of the map. Approaching the door will trigger a cutscene. After the cutscene, check the nearby Weapon Crate for a Hammer assault rifle, then get on the cargo elevator and activate the console. After activating the lift, a cutscene will trigger and a familiar foe will engage Wolfpack. To get rid of Mr. X, shoot the glowing spot on its chest until it falls off of the lift; run around the lift avoiding its melee attacks and use the Ammo Crate to replenish ammunition. Once Mr. X is knocked off, the lift resumes for a short while until a group of Lickers attacks. Kill them to cause the lift to move; look up and move towards the opposite ends of the lift to avoid the gouts of fire from the sides of the elevator shaft. After passing the third flame jet, Mr X returns. Use the same tactics as before to knock it off the elevator again; once its gone the elevator will continue up. Once the elevator has reached ground level, exit the elevator to trigger a cutscene and end the mission.